Don't know why the one with slower speeds is most expensive, it's probably a mistake on newegg's part.
This is the best one:
It's the 7800GT CO, which has a special lifetime warranty that gaurentees to replace it for any reason (short of physical damage) free of charge, even if you kill it with OCing. I just ordered one to replace my 6800GT that had problems, should be here wednesday or tuesday. And why are you looking at a 7800GT when you have a GTX? :shocked: